Abstract: The postulation of Dark energy and Dark matter on the basis of observationalresults does not end the mystery of their existence. Theoretically new insightsinto dark matter have been achieved analyzing recent experimental data from thecosmic ray physics. It has been shown that, if the dark matter is a hiddenscalar field, then it is not only possible to explain the ATIC-PPB BETS excessbut also the observed dark matter abundance naturally and simultaneously. Beingmotivated, mainly by the assumption of hidden scalar field and some associatedworks, we consider the Modified Chaplygin Gas for some thermodynamicalanalysis. The point that if the scalar field is assumed to oscillate before thereheating was not completed, i.e., T R <= 10^10 GeV, the abundance of darkmatter would be diluted by the entropy production during reheating indicatesthe importance of thermodynamical analysis. We, assuming the properties ofModified Chaplygin Gas, derive an expression for the second law ofthermodynamics. It is observed that it also sheds some new lights onGeneralised Second Law.